1. Field of the Invention
The present invention relates to a multi processing system composed of more than two data processing units such as a master and slave CPU system having one master, CPU and more than two slave CPU which are arranged in a hierarchial structure.
2. Description of the Prior Arts
In an apparatus having a plurality of control objects such as input devices and output devices, it is well known to divide the apparatus into a number sections and to provide a master control unit and a plurality of sub control units so that each sub control unit controls independently any one of the sections assigned to the respective sub control unit under the supervision by the master control unit. The arrangement mentioned above enables to decreases the burden of the respective sub control units and improves improve the reliability of the control system. If the sub control units are simple, there is provided a condition control table for each sub control units in the master control unit and each sub control units cannot control the corresponding control object or objects so as to realize the data sent directly from the master control unit.
In a master and slave CPU system as mentioned above, in the apparatus in which with several control modes and where the combinations of control objects to be operated on are different for each control modes, it is necessary to update the contents of the condition control table at the time of changing of the control mode and it is necessary to send signals to the sub control units so as to enable only the control objects designated in the new mode. In a conventional master slave CPU system, the previous control conditions of all of the control objects are compared with the current conditions which are used in the newly selected control modes and the master CPU sends a keeping signal instructing the slave CPUs to keep the present control condition control conditions when the of the comparison coincide and sends a reversing signal instructing the slave CPUs to update when the control condition of the previous control mode is different from that of the current condition.
However, in the conventional master slave CPU system, if once the control mode is changed, after all of the control conditions of the previous control mode are compared with all of those of the current control conditions, and the master CPU send the keeping signal or reversing signal to the slave CPUs with respect to all of the control objects, whereby the control processing in the master control CPU is redundant and a long time is consumed.